Advances in semiconductor manufacturing technology have allowed for reduction in device feature sizes, increases in IC integration levels, and the implementation of devices with processing speeds of CPUs in the gigahertz (GHz) range. The circuit density and operating speed of device packaging may need to be adapted to accommodate these device developments. The electromagnetic compatibility of device packages accommodating these high frequencies may be a dominant factor affecting packaging developments.
One of the problems of electromagnetic compatibility is crosstalk. Crosstalk generally is the unwanted propagation of noise or interference between transmission lines. On a semiconductor device these transmission line terminations are typically termed pins or ports. Crosstalk is a measure of the effect of a signal on one pin influencing the signal on other pins. Crosstalk is usually expressed in dB and is associated with a signal frequency. In general, crosstalk increases as the signal frequency increases. The pins of the semiconductor device are typically coupled to a package. The package is more easily connected to circuit boards or other device systems.
A chip scale package (CSP) is a type of integrated circuit chip carrier that has no pins or wires but uses contact pads instead. To be considered a CSP, a package must have an area no greater than 1.2 times that of the integrated circuit chip being packaged.
The die may be mounted on an interposer upon which pads or balls are formed, as in ball grid array (BGA) packaging and flip chip BGA packaging, or the pads may be etched or printed directly onto the substrate, resulting in a package very close to the size of the silicon die. A package in which the entire assembly process is completed at the wafer level is termed a WLCSP (Wafer-level Chip Scale Package). Similar to the FBGA (Fine Ball Grid Array) package, a WLCSP package has pin connections arranged into a grid on the rear face of the package. In contrast to the FBGA, the WLCSP package size is smaller and closer to the size of the chip. However, as the package size decreases, the crosstalk between pins, especially at high frequency, may cause system instabilities.